I wouldn't do either just yet. Try to joining a writer's guild/league/group, there are usually tons of members hoping to swap manuscripts and exchange ideas and or editorial criticism. It can be a really helpful, free way of getting your work that much more polished.
Then yes, if you think an independent editor is what you need than you contact him/her first. Beware, however because this is one of the shadier parts of the industry. Just because someone claims to be an editor (or agent for that matter) doesn't mean they are. Just do thorough research and you should be fine.
It's important to note that almost every legit agent will get your novel brushed up for you, most of them started out as editors and major publishers so they typically do it themselves. So if you think your novel has a chance of getting picked up with professional editing, then your new agent will probably help you in that arena as well as sales.
As far as your age goes, technically you never have to tell them. There's an issue called age discrimination and it's illegal. It usually applies to seniors, but you'd be covered also (assuming). That being said, just being up front and honest with people will get you a long way, but you probably won't get picked up by anybody at 16. That's just the way things go. However, it would be a valuable experience, and you may make some great contacts by querying so take the chance, I say.
Just be prepared for the reality of your situation, and best of luck to you!